keeps plugin config on reenablement (#35545) (#35581)

* keeps plugin config on reenablement

* fixes local config patch on plugin reenablement

(cherry picked from commit c9a4092ac0a20351e3c2e0ac0cb593cc28b5bc0e)

Co-authored-by: Carlos Garcia <carlos.garcia@mattermost.com>

server/channels/api4/config.go

@@ -347,6 +347,11 @@ func patchConfig(c *Context, w http.ResponseWriter, r *http.Request) {
 		c.App.HandleMessageExportConfig(cfg, appCfg)
 	}
 
+	// Treating an empty plugins map as nil preserves the existing configs.
+	if len(cfg.PluginSettings.Plugins) == 0 {
+		cfg.PluginSettings.Plugins = nil
+	}
+
 	updatedCfg, err := config.Merge(appCfg, cfg, &utils.MergeConfig{
 		StructFieldFilter: filterFn,
 	})

server/channels/api4/config_local.go

@@ -116,6 +116,11 @@ func localPatchConfig(c *Context, w http.ResponseWriter, r *http.Request) {
 		c.App.HandleMessageExportConfig(cfg, appCfg)
 	}
 
+	// Treating an empty plugins map as nil preserves the existing configs.
+	if len(cfg.PluginSettings.Plugins) == 0 {
+		cfg.PluginSettings.Plugins = nil
+	}
+
 	updatedCfg, mergeErr := config.Merge(appCfg, cfg, &utils.MergeConfig{
 		StructFieldFilter: filterFn,
 	})

server/channels/api4/config_test.go

@@ -950,6 +950,72 @@ func TestPatchConfig(t *testing.T) {
 		_, _, err = th.SystemAdminClient.PatchConfig(context.Background(), &model.Config{})
 		require.NoError(t, err)
 	})
+
+	t.Run("should preserve plugin configs when toggling plugin enable off then on", func(t *testing.T) {
+		// Have some plugin settings setup
+		th.App.UpdateConfig(func(cfg *model.Config) {
+			cfg.PluginSettings.Enable = model.NewPointer(true)
+			cfg.PluginSettings.Plugins = map[string]map[string]any{
+				"com.example.oauth-plugin": {
+					"clientid":     "test-client-id",
+					"clientsecret": "test-client-secret",
+				},
+			}
+		})
+
+		// First PATCH: disable the plugin subsystem
+		disablePatch := &model.Config{}
+		disablePatch.PluginSettings.Enable = model.NewPointer(false)
+		disabledResponse, _, err := th.SystemAdminClient.PatchConfig(context.Background(), disablePatch)
+		require.NoError(t, err)
+		// The sanitized response returns an empty Plugins map when plugins are disabled
+		assert.Empty(t, disabledResponse.PluginSettings.Plugins)
+
+		// Second PATCH: re-enable plugins using the response from the first PATCH
+		disabledResponse.PluginSettings.Enable = model.NewPointer(true)
+		_, _, err = th.SystemAdminClient.PatchConfig(context.Background(), &model.Config{
+			PluginSettings: disabledResponse.PluginSettings,
+		})
+		require.NoError(t, err)
+
+		// Plugin configs must survive the round-trip unchanged
+		storedCfg := th.App.Config()
+		require.Contains(t, storedCfg.PluginSettings.Plugins, "com.example.oauth-plugin")
+		assert.Equal(t, "test-client-id", storedCfg.PluginSettings.Plugins["com.example.oauth-plugin"]["clientid"])
+	})
+
+	t.Run("local client should preserve plugin configs when toggling plugin enable off then on", func(t *testing.T) {
+		// Have some plugin settings setup
+		th.App.UpdateConfig(func(cfg *model.Config) {
+			cfg.PluginSettings.Enable = model.NewPointer(true)
+			cfg.PluginSettings.Plugins = map[string]map[string]any{
+				"com.example.oauth-plugin": {
+					"clientid":     "test-client-id",
+					"clientsecret": "test-client-secret",
+				},
+			}
+		})
+
+		// First PATCH: disable the plugin subsystem
+		disablePatch := &model.Config{}
+		disablePatch.PluginSettings.Enable = model.NewPointer(false)
+		disabledResponse, _, err := th.LocalClient.PatchConfig(context.Background(), disablePatch)
+		require.NoError(t, err)
+		// The sanitized response returns an empty Plugins map when plugins are disabled
+		assert.Empty(t, disabledResponse.PluginSettings.Plugins)
+
+		// Second PATCH: re-enable plugins using the response from the first PATCH
+		disabledResponse.PluginSettings.Enable = model.NewPointer(true)
+		_, _, err = th.LocalClient.PatchConfig(context.Background(), &model.Config{
+			PluginSettings: disabledResponse.PluginSettings,
+		})
+		require.NoError(t, err)
+
+		// Plugin configs must survive the round-trip unchanged
+		storedCfg := th.App.Config()
+		require.Contains(t, storedCfg.PluginSettings.Plugins, "com.example.oauth-plugin")
+		assert.Equal(t, "test-client-id", storedCfg.PluginSettings.Plugins["com.example.oauth-plugin"]["clientid"])
+	})
 }
 
 func TestMigrateConfig(t *testing.T) {